1. Field of the Invention
The present invention relates generally light based to touch screen displays, and more particularly, to an apparatus and method for a folded optical element waveguide that allows a minimum width bezel to be used around the perimeter of the touch screen display.
2. Description of the Related Art
User input devices for data processing systems can take many forms. Two types of relevance are touch screens and pen-based screens. With either a touch screen or a pen-based screen, a user may input data by touching the display screen with either a finger or an input device such as a stylus or pen.
One conventional approach for providing a touch or pen-based input system is to overlay a resistive or capacitive film over the display screen. This approach has a number of problems. Foremost, the film causes the display to appear dim and obscures viewing of the underlying display. To compensate, the intensity of the display screen is often increased. However, in the case of most portable devices, such as cell phones, personal digital assistants, and laptop computers, high intensity screens are usually not provided. If they are provided, the added intensity requires additional power, reducing the life of the battery of the device. The films are also easily damaged. These films are therefore not ideal for use with pen or stylus input devices. The motion of the pen or stylus may damage or tear the thin film. This is particularly true in situations where the user is writing with a significant amount of force. In addition, the cost of the film scales dramatically with the size of the screen. With large screens, the cost is therefore typically prohibitive.
Another approach to providing touch or pen-based input systems is to use an array of source Light Emitting Diodes (LEDs) along two adjacent X-Y sides of an input display and a reciprocal array of corresponding photodiodes along the opposite two adjacent X-Y sides of the input display. Each LED generates a light beam directed to the reciprocal photodiode. When the user touches the display, with either a finger or pen, the interruptions in the light beams are detected by the corresponding X and Y photodiodes on the opposite side of the display. The data input is thus determined by calculating the coordinates of the interruptions as detected by the X and Y photodiodes. This type of data input display, however, also has a number of problems. A large number of LEDs and photodiodes are required for a typical data input display. The position of the LEDs and the reciprocal photodiodes also need to be aligned. The relatively large number of LEDs and photodiodes, and the need for precise alignment, make such displays complex, expensive, and difficult to manufacture.
Yet another approach involves the use of polymer waveguides to both generate and receive beams of light from a single light source to a single array detector. These systems tend to be complicated and expensive and require alignment between the transmit and receive waveguides and the optical elements and the waveguides. The waveguides are usually made using a lithographic process that can be expensive or difficult to source. In addition, the waveguides are typically flat. As a consequence, the bezel around the display is relatively wide. See for example U.S. Pat. No. 5,914,709.
Accordingly, there is a need for a folded optical element waveguide that allows a minimum width bezel to be used around the perimeter of a touch screen display.